Gas turbine plant having a plurality of flame tubes and axially slidable means to expose same



1952 a. B. R. FEJLDEN ,384

' GAS TURBINE PLANT HAVING A PLURALITY OF FLAME TUBES Y AND AXIALLY SLIDABLE MEANS '10 EXPosEsAME I Filed Jan. 14. 1946 7 Sheets-Sheet 1 a D 6 N Fig. l.

MIN 1908597 FE/ADE/V,

- Inventor B Rum R y Attorney Oct. 21, 1952 FE|| DEN 2,614,384

GAS TURBINE PLANT HAVING A PLURALITY OF FLAME TUBES AND AXIALLY SLIDABLE MEANS T0 EXPOSE SAME F-iled Jan. 14, 1946 7 Sheets-Sheet 2 Fig. a.

Q y v mud R M Attorney e. B. R. FEILD EN men/ fizzy m4 ROBMT' F5! 02 M 8 R on.

GAS TURBINE PLANT HAVING A PLURALIT AND AXIALLY SLIDABLE MEANS TO EXPO Filed Jan. 14, 1946 Oct. 21,

B. R. FEILDEN 2,614,384 T HAVING A PLURALITY 0F FLAME TUBES AND AXIALLY SLIDABLE MEANS ,TO EXPOSE SAME 14, 1946 7 Sheets-Sheet 5 Oct. 21, 1952 GAS TURBINE PLAN Filed Jan Attorney G. B. R. FEILDEN T HAVING A PLURALITY OF FLAME TUBE Oct. 21, 1952 GAS TURBINE PLAN 5 AND AXIALLY SLIDABLE MEANS TO EXPOSE SAME Filed Jan. 14, 1946 7 Sheets-Sheet 6 Inventor Jil-Ialll. l. .I 1 -Ill-llllll M R By Attorney Oct. 21, 1952 5, FElLDEN 2,614,384

GAS TURBINE PLANT HAVING A PLURALITY OF FLAME TUBES AND AXIALLY SLIDABLE MEANS T0 EX POSE SAME Filed Jan. 14, 1946 7 Sheets-Sheet 7 Inventor A from ey Patented Oct. 21, 1952 GAS-TURBINE PLANT Av G A rLURALITY 0F TUBES, AND AXIALLY SLIDABLE 0. EXBQS SAME- Geoffrey Bertram. Robert Eeilden, Lutterworth, Eng an ss gnor to. Power; Je s. (R sear h. and. D re crment). ain-cit d; and n England 'Appfica January 14, 1946, Serial No. 641,144; In Great Britain January 16,1945

This invention relates to gas turbine power plants of the kind: comprising a coaxial, com-.1 pressor and turbine axially spaced in tandem and accommodating in. the space between them a combustion system through which working fluid;

is-supplied; by-the compressor to the-turbine with a general direction of flow in the. axial direction.

Where such a machine isto be used as a powerunit, for example. forthe propulsion of aircraft, various attributes are. desirable; For example the unit should be kept as compact and as light as possible, whilst maintenance and replacement or components and probably periodical inspece. tion of internal components should be facilitated. It is also desirable that the disposition of parts which are liable to fluctuations of. temperatureor which operate with a temperature gradient through. them should be such as'ta allow for or cope with relative expansions and contractions, and distortions, without. adverse effect. The various aspects. of the present. invention seekto provide such attributes as. well as. others. ti'cul'ar objects of the. invention .as applied to a gas turbine power unitv for aircraft are to. achieve a symmetrical construction capable of withstanding the. requisite loads-affordinggood combustion properties without undue pressure loss and affording accessibility for replacement or inspecttion. A more specific, object in a. particular example is to provide a. combustion arrangement which is. conveniently disposed in relationto. a complete power unit.

The, invention is based on the. conception of using, in a gas turbine power unit. of the. kind referred to, a combustion system comprisingan annular aircasing providing a flow. path from the compressor to. the turbine, and a plurality of individual combustion chambers. separately mounted on the plant structure within and dis; tributed annularly around said aircasing in which the actual combustion takes place. In associa.-.-: tion with this conception, the invention proposes that the outer wallof said aircasing should be a unitary circular structure ct greater: diameter than at least. one of'the. major components .(turs. bine or compressor) at either end thereof-and should. be constructed and mounted soflthat it can be withdrawn over such component. by axial movement. toexpose the combustion chambers, the arrangement being such that the latter can then be released and removed; orreplaced indi vidually by virtue-of" their separatev mountings, while, the outer v wall ofthe. aircasing retains its maximum value as a stress=oarrying member. in use by virtue of its unitary: circular structurel Par- The combustion chambers should of course. be so supported and shaped that after obtaining access thereto. by displacement of the outer wall of said air'casing, for example'axially as aforew. said, they may be released and removedor re-. placed individually, said combustion chambers. being separately supported by the structure. of the. plant and the relationship and shaping; of said chamberstheirconnections, and. th adjacent components, all being .such as to accommodate. such operations. such an arrangement is facili-.

tated by reasonof thefact that since the com--. bustion chambers arexnot called upon to sustain amajor pressure difference, they may belof rela-. tively light construction and mounted ina reads ilyreleasable. and non-gastight manner. In this connection, an associated feature of the invention resides in the individual mounting. of each axially directed. combustion element in the annular airs casing by means which support the element at its, ends, but permit its disengagement by axial movement, together with means which locate the element against, such axial movement in use, so that after releasing such locatingmeans the combustion element may be removed'by manipulation commencing with an axial disengaging move--.

ment.

In av preferred application, the various features of the invention are embodied, individually .or jointly, in a gas turbine power plant comprising a multisstage compressor with air outlets ar-. ranged symmetrically about its shaft axis and directed in a general sense axially, and an axial flow turbine spaced axially from the compressor and in tandem therewith. While .the aircasing walls will normally be of circular crosssection, and the space between them truly annular, the use of other equivalent sections would be within the spirit of the inven-. ion, and the expression annular is accordingly to; be interpreted as including non-circular closed sections bounded by inner and outer spaced enclosing walls.

Other features of the invention include the making of provision forthe circulation of cooling air, and for variation in the shape or dimensions of the, combustion elements with temperature. Thesaiasjwellas other more detailed construe! tional forms, will now. be more. fully described with reference to the accompanying drawings, Which illustrate by way of example two aircraft gas turbine units, embodying the invention, and in, which:

Figures 1 and la constitute together an elevation in half longitudinal section showing the general arrangement of an aircraft jet propulsion gas turbine power unit embodying the features of the invention in one constructional form;

Figure 2 is a detail sectional elevation to an enlarged scale illustrating the construction of the aircasing of the power unit illustrated in Figure l, and the construction and mounting of flame tube combustion elements and air jackets therein;

Figure 3 is a further enlarged detail illustrating the mounting of a flame tube combustion element on a burner;

Figures 4 and 4A constitute together an elevation of another jet propulsion gas turbine power unit illustrating the general arrangement thereof in part longitudinal section in the region of the aircasing, which is of a modified form as compared with Figures 1 and 1a;

Figure 5 is a detail sectional elevation to an enlarged scale illustrating the modified construction of aircasing and construction and mounting of flame tube combustion elements embodied in Figure 4A.

In the example illustrated in Figure 1, the power unit comprises generally a multistage axial compressor I, an annular combustion arrangement 2, a turbine 3 exhausting into a reaction jet passage 4, a thrust-augmenting ducted fan 5 associated with the turbine 3 and operating in a supplementary reaction jet passage 6 coaxially surrounding the passage 4, and a shaft I common to the compressor I and turbine 3 through which the latter drives the former, and with respect to which the entire engine is arranged in a symmetrical circular manner, the said shaft incorporating a flexible coupling Ia having resilient flange elements and a tension element which resists the opposed end thrusts developed by the compressor and turbine. The forward end of the unit when installed, is enclosed by a fairing 8 as may be appropriate to the aircraft concerned. At the forward end of the compressor is carried a gear box for driving accessories which derives its power from the shaft I.

The compressor I has a rotor built up from a plurality of separate discs each carrying peripherally a row of compressor blading, whilst the stator blades extend inwardly from an outer casing 9 which, with the front and rear walls I0, II, in which bearings are provided for the shaft 1, defines an annular inlet at I2 and outlet at I3, of which the latter is extended axially by inner and outer annular walls I4, I5 which, with radial walls I6 therebetween form a series of axially directed diffuser channels all opening at an annulus defined by two concentric flanges of the walls I4, I5. To the inner flange (see more particularly Figure 2) is attached a hollow structure or member I! of circular cross section which encloses the shaft I and extends coaxially therewith towards the turbine 3. Towards its rear end, the member I! is rigidly attached to the apex of a frusto-conical member I8 the rearward or base rim of which provides the inner support of the turbine entry nozzle annulus I9, between which and the inner wall of the passage 5 is a frusto-conical bracing annulus [8a.

In the construction illustrated, the turbine, generally indicated at 3, comprises a first or compressor-driving turbine having two axially spaced bladed rotors 20 fast on the shaft 1, and a second turbine having one bladed rotor 2| which is arranged forwardly of the rotors 20 andhas a bearing sleeve 20a by which it is rotatably mounted through axially spaced bearings 20b on a tubular member formed by a rearward extension 4 I Ia of the structure I! already referred to, the said extension Hot and member I'I being in turn spaced from the shaft I and supporting it by axially spaced bearings I'Ib as indicated. The blading of therotor 2| is connected to a peripheral rim 22 which extends'rearwardly to form both a tip shroud for the blading of the rotors 20, and a support for a second ring of blades 2Ia. These blades extend radially inwardly, like interstage stator blading. There is no fixed nozzle ring or interstage stator blading associated with the first turbine, the function of such parts. being performed by the first and second rows of blading of the second turbine, which accordingly rotates contrarily to the first. The function of the second turbine is to drive the two stage ducted fan 5 whose rotatable blades 5a are carried by a drum 23 whose forward end is supported on the rim 22 of the second turbine by a frusto-conical member 24, and whosestator blades 5b,.are fixed to the main structure of the ducting. forming the passage '6, the inner wall of which is braced from the nozzle ring of the second turbine by the frusto-conical member vIila. It follows from this construction that the torque of the second turbine is transmitted outwardly to the fan drum 23 so that the fan will augment the flow of air in the duct 6 derived from its forwardly facing entry. The ducts l, 6 unite at some distance aft of the fan 5 and in the intervenirfg length of the duct 6 fuel combustion means 26 are provided further to energise the airflow, preferably so as to accelerate it to the velocity of the turbine exhaust stream in the passage 4 before the two streams emerge as a single propulsive jet.

The hollow member I! constitutes the inner air pressure-sustaining wall of an axially extending annular aircasing, the outer pressure-sustaining wall of which is formed by a tubular member 27 detachably secured at its forward end to the outer flange of the compressor outlet annulus defined by the walls l4, I5 and at its rear end to a frustoconical member 25 whose apex is secured to the turbine nozzle ring I9. The member 27 is of such internal diameter that when its fastenings are released it may be slid forwardly over the compressor casing 9. The members 21, II, have mounted thereon in spaced relationship thereto, sheet metal liners 28, 29, to provide anair jacket for the inner and'outer walls of the aircasing, these liners being arranged at their ends to pick up a proportion of the incoming air stream and discharge it to the turbine after flowing through the respective air. jackets. In this connection, in order that it shall not interfere withthe axial withdrawal of the outer wall 21, the liner 28' makes loose overlapping joints with liner parts 2811 which are mounted on parts of the structure which remain fixed when the member 21 is removed.

Between the walls I1, 27, and in the annular cavity they enclose, is provided an annularly'arranged series of axially extending flame tubes so dimensioned as to Permit freedomof airflow around and among them. The main body 30 of each flame tube is cylindrical and has at its upstream end a frusto-conical closure whose apex engages axially with, and is supported by, the protruding end of' a cylindrically shaped burner or fuel nozzle 3| which is coaxial withthe flame tube and is mounted upon one of the diffuser walls I6 of the compressor outlet annulus. A suitable form of such a construction is illustrated in Figure 3 in which the burner body 3| is bolted b rs 30a so as to lie j s wi hin .andspac o one oi heuiffus r wa ls i-oi the c mpressor fl me tube is retained against involuntary dis? placement by making thread d ngagem nt with the no z e 3 l as sh wn, o by oth suitab emeans, and prov sion is ma e y a passae tld-iorthe ent y o combust on air throu h and a ound the noz le. ,The fl me tube W ll s also-pe fo ated and provided with appropria e guidesnd babies as may e f und combu tion e downstream end of the cylindiiicalbody w tube is supported, for example by flexiblet th circu a ps ream end of out et wh ch. tapers the down tream dir ctio fla tened s ct on c rresponding to a e ment of the annu r n z le rin l9 of the turbine-J Space is left around the outside of each outlet-chute .3-2 .for the passage of some air to the turbinenozzle so that this air cools the wall of the chute and.

' being itself heated in the process'ultimately joins thev hot gases which are entering the turbine. The chute .32 is located and supported -by a substan? tially radial strut-like element 3.3 passing -there-. through and also through the liners 281a, 29, "a nd inner and outer aircasing members 18, 25,'to a11 of which parts the strut is secured, as 'by welding.

, Preferably the primary purpose oflthe struts 33,

comprcsscroutlet annulus and the turbine nozz e ring forms a rigid By :making the parts ll. 21: 1:8,25 serve this dual purpose an appreciable saving of weight can be achieved without sacrie flee of rigidity: and strength.

The use of an annular .aircasing enclosing a space around the 1 compressor turbine Shaft .I

, bounded at its rearward end by the turbine rotor lends itself admirably to the provision of a dis tributing system for, cooling" air, additional to that already referred to in connection with the internal construction-of the aircasi'ng and flame tubes, which willvassist in avoiding gas leakage, local distortions andexcessive local temperatures, and to a cor'isiderablev extent render uniform the temperature distribution throughout the engine. One such system isillustratedin Figures 1 and 2; in which the wall formed by the innermember I! of the aircasing i's'made hollowand, being con nected by a pipe .35'to a suitable point on the compressor to receive compressed air therefrom, distributes it as indicated bythe arrows inFig ure 2. The hollow of the member I! forms air passages 36 (see Figure 2) which supply air to the turbine bearings and also with the chamber bounded by the member I8 and the face and journal sleeve of the turbine rotor 21. This chamber contains a stationary sheet metal liner 3'! of annular form which constrains the air flow to follow the surface of the turbine rotor parts, the'air eventually escaping through the flame tube struts 33 to the inlet of the augmenter duct. In addition, the shaft 7 is made hollow and transmits air to'the inner'and rear faces of the rotors whence which are provided at intervals around the an-.- n'ulus of the aircasi-ng, is to maintain the concen tricity ofthe' aircasing part I8, 25, but it may also be made hollow andthus provide a com- Alternative methods of supporting the outlet chute 32 may be adopted, but in any case the support is so contrived as to permit longitudinal a-nd radial expansions without bodily displacement of w the fiametube and without" imposing specific stresses thereon or on' any ofthe related parts.

To remove any flame tube body 30, the outer wall 21 of the aircasi-ngis cast loose and displaced axially over the'compressor'casing 9, whereafter it escapes to the turbine gas stream. The air coming direct from the compressor is'arranged to be at a slightly higher pressure than that in the turbine so that the tendency is for the air to flow into the turbine rather than for gas to es ape from the latter.

I By means of the air "systems described above, or modifications thereof, the various cavities and regions of the engine may be supplied with compressed air in such a wayas to effect cooling and oppose any tendency to gas leakage, although gas seals will still be employed where necessary as, for example, at 40 in the figures.

In the construction .of airca'sing illustrated in outer member 25, are formed by relativel subi stantial castings'; 'according to a further feature the threaded or other attachment of the flame I tube body to the burner 3| is freed and the flame tube body shifted axially towards the turbine to free it completely fromthe burner (a movement which is allowed for in the spacing of the downstream end of the body 30 from any axiall-yob struoting parts). The body 30 may then be tilted sufficiently to allow it to be withdrawn.-

As an alternative theflame tube body 30 may be left attached to the burner, and the latter unbolted so that it can be withdrawn from its mounting by the axial movement of .the flame tube. either case, the burner itself is in essence the support of the flame tube at its upstream end, whilst the means which relate it to the outlet chute or to the main aircasing structure (which permit ex,

carrying element which with the flanges 01- "the of the invention-"these parts are fabricated from sheet'metal whilst still retaining the features that the airca'sing, in addition to being the air pressure-sustaining element of the combustion arrangeme'nt, "constitutes a major stress-carrying structure forming with the compressor and turbine casings a substantially rigid unit.

- S ch a modified form of aircasing is illustrated in Figures 4, 4A and 5 in which parts similar to those in Figures 1 and 1a have like reference numerals, as applied to another form of power unit from that appearing inFigures land 1a, and which, apart from the aircasing construction, differs therefrom principally in that the compressor output passes first through outwardly directed passages to a two part outlet annulus Et'before being discharged in a generally axial direction into the combustion arrangement; that the contrarotating rotor of the turbine and its associated ducted fan augmenter are omitted; and that the forward end of the shaft 1 is used to drive, through a concentric epicyclic reduction gear, the coaxial shafts of a pair of contrarotat ing airscrews. i

The aircasing in this instance comprises an inner member I! of frustoconioal form having internal strengthening ribs 53. The said inner member H is supported at its forward end by oppositely tapering radially inwardly and outwardly directed frustoconical elements 54, 55 secured thereto'and to the rear wall ll of the compressor housing, and at its rear end by a somewhat similar arrangement of frustoconical elements 55; of which the inner one is secured to the housing of the turbine rotor bearing 58 which, as in Figure l, is arranged forwardly of the rotor for the better access of cooling air, and the outer one is secured to the inner part of the turbine nozzle ring IS. The elements 11, 54, 56, thus completely enclose an inner chamber within the aircasing. The outer member of the aircasing comprises a member 2'! of cylindrical-conical form having its largest diameter at its forward end, where it is secured to the compressor outlet annulus 5|, and tapering to its rear end, where it is secured to the base rim of a generally frustoconical element 59, the apex of which is secured to the outer part of the turbine nozzle ring l9. Each of the mentioned parts of the aircasing is fabricated from relatively thin sheet metal to form a tubular or dished annular element of considerable stiffness, so that when they are united a backbone structure is obtained having a high degreev of rigidity combined with light weight which, when secured to the compressor and turbine, forms therewith a substantially rigid unit.

Where a sheet metalelement is to be joined to external pressure in the annular aireasing. By this means, the sheet metal inner structure I1, 54, 55, may be made much lighter, and with less attention to inner stiffening, than would otherwise be the case; in fact, the feature is of great importance in enabling the maximum advantage to be taken of the lightness of structure offered by the use of sheet metal; By providing suitable outlets, compressed air within the said inner chamber may be utilised to provide air'cooling circuits, such as those indicat ed by arrows in the drawing, to the compressor and turbine rotors and' the shaft bearings. A's indicated in the drawing, the internal pressure may be obtained by tapping air under pressure from theaircasing by means of a pipe 6| connected tothe inner chamber, theair passing through acooler 62.

'1-.-A gas turbine power plant comprising a compressor assembly consisting of a compressor rotor and an enclosing stationarystruc'ture, a

another'part, it is provided with a thickened flange, as indicated in thedrawing, by Welding on to the sheet metal a strip-0., more substantial metal. l .l v

As in the embodiment illustrated in Figures 1 and 1a, the outer wall 2? of the aircasing is axially removable, although in this case rearwardly, to expose the combustion system, which again comprises a series of flame tubes spaced around the hollow annulus formedby the aircasing. As before, the flame tubes comprise a generally cylindrical body 30 forwardly closed by a conical end engaging the fuel burner or nozzle 3! and supported at the rear end by an outlet chute 32 positionedby a hollow strut 33 passing therethrough. In place of the complete airjacketing of the aircasing by liners corresponding to those in the previous construction, the com.- pressor discharges through sheet metal outlet nozzles ED which at their upstream ends are of flattened section to fit a segment of the annular outlet of the compressor, and merge downstream into a cylindrical shape which encloses for a substantial distance the upstream end of one flame tube and is spaced from it to allow the passage of. air. 1

The flame tube arrangement just described again provides for the ready individual removal of the tubes after access thereto has been obtained by displacing the outer wall 21, the method of removal being the same as described in relation to Figures 1 and 1a except that it is also necessary to displace the nozzles 60 rearwardly over the upstream end of the corresponding tube body, the clearances between each nozzle and body-being made such that when this hasbeen done both nozzle and body can be tilted outwardly without fouling the burner 3 I.

A feature of the design illustrated in Figures 4, 4A and 5 is that the entire inner chamber defined by the members I1, 54, 56 is maintained under pressure in order to compensate for the turbine assembly consisting of a t'urbinef rotor coaxial with the compressor rotor and'an enclosing stationary structure, a shaft "carrying saidrotors; a combustion system accommodated between the compressor and turbine. assemblies, said combustion system includingan annular air-casing formed byv an inner and'outer tubul'ar vmember mounted coaxially with' 'the shaft and. defining between'thema flow path from said compressor to said turbine. extending generallyin an axial direction,and a plurality of flame tubes mounted within and annularly distributed around said air-casing, said outer tubular member being-a unitary'structure, theinternal diameter of which over at least part f its length adjacent oneencL; is greater than the external diameter of 1 the stationary structure adjoining said end of the ytubulanmember, the

external diameter of said stationary; structure being less than the internal diameterjef-said tubular member from a point adjacent saidend;

of said tubular member to --apoint located a substantial distance 111. a direction axially-away from said tubular member, whereby said -tubular member-canbe withdrawn over said st tionary structureito expose the flame tubes.

2. A gas turbine power; plant comprising a compressor assembly consisting of. a compressor rotor. and an enclosingstationary structure, a turbine assembly consisting of a turbine rotor coaxial with the compressor rotor .andan enclosing stationarystructure, a shaft carrying said rotors, bearings .in each said. stationary structure supporting said shaft, .a combustion system accommodated between the compressor andturbineassemblies, said combustion system including anannular air-casing formed by an inner and anoutertubular member mounted coaxially withtheshaft. and defining between them a 'fiowpath'f'rom ,said compressor to said turbine extending generally in an axial direc-. tion, and a plurality. of' flame tubes mounted within and "annularly' distributed around said air-casing, said outer tubular member'being a unitary structure, theinternal'diameter of which over. at least part of its length adjacent one end is greater than the external diameter of the stationary structure adjoining said end of the tubular member, the external diameter of said stationary structure being less than the internal diameter of said tubular mem'berfrom a point adjacent'said end of said tubular member to a point located a substantial distancein adirec- 9 tion axially away from said tubular member, whereby said tubular member can be withdrawn over said stationary structure to expose the flame tubes.

3. A gas turbine power plant comprising a compressor assembly consisting of a compressor rotor and an enclosing stationary structure, a turbine assembly consisting of a turbine rotor coaxial with the compressor rotor and an enclosing stationary structure, a shaft carrying said rotors, bearings in each said stationary structure supporting said shaft, a combustion system accommodated between the compressor and turbine assemblies, said combustion system including an annular air-casing formed by an inner and an outer tubular member, mounted coaxially with the shaft and defining between them a flow path the external diameter of the stationary structure adjoining said end of the tubular member, the external diameter of said stationary structure being less than the internaldiameter of said tubular member from a point adjacent said end of saidtubular member to a point located a substantial distance in a direction axially away from said tubular member, whereby said tubular member can be withdrawn over said stationary structure to expose the flame tubes.

4. A gas turbine power plant as claimed in claim 3, wherein each flame tube is mounted in the annular air-casing by means which support the flame tube at its ends, but permit its disengagement by axial movement, together with means which locate the flame tube against such axial movement in use, so that after releasing such locating means the flame tube may be removed by manipulation commencing with an axial disengaging movement.

5. A gas turbine power plant as claimed in claim. 4, wherein the combustion system comprises, in respect of each flame tube, an axially directed burner body mounted on fixed structure '10 at the upstream end of said annular aircasing, and a discharge chute which is mounted on fixed structure at the downstream end of said aircasing and has an outlet shaped to form a segment of an annulus corresponding to the turbine inlet annulus, said discharge chutes having peripherally spaced individual entries each corresponding to one flame tube and their outlets collectively forming a virtually continuous annulus, and each flame tube comprising an axially extending tubular sheet metal body whose upstream end releasably engages said axially directed burner body with allowance for axial movement upon release and whose downstream end is radially supported and located by spigotting engagement with the entry of a discharge chute with provision for axial movement relative thereto.

6. A gas turbine power plant as claimed in claim 3, wherein said withdrawable outer wall of the aircasing has, within the annular cross section of said casing, a liner mounted on and spaced therefrom to be removable therewith and to constitute an air jacket, said liner being con- 'structed to divert through said jacket a part of the air stream entering the aircasing.

'7. A gas turbine power plant, as claimed in claim 6, wherein the aircasing has, at its inlet and outlet, fixed liners spaced from its outer wall to constitute an air jacket and guides diverting and discharging a part of the air stream passing through said aircasing, said fixed liners, when the aircasing is assembled, co-operating with the liner mounted on the withdrawable wall to constitute with that liner a continuous air jacket extending from the inlet to the outlet of the aircasing.

GEOFFREY BERTRAM ROBERT FEILDEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS v Date Number Name 2,401,826 Halford June 11, 1946 2,408,743 Elliott Oct. 8, 1946 2,432,359 Streid Dec. 9, 1947 2,468,461 Price. Apr. 26, 1949 2,469,439 Lundquist May 10, 1949 

